Control method for an electric pump adapted to supply pressurised operating fluid for an automatic transmission

ABSTRACT

A control method for an electric pump adapted to supply pressurised operating fluid to actuators of an automatic transmission in order to cause the opening/closing of the clutch and the selection and engagement of the gears, in which the stage of supply of a voltage to the motor of the electric pump is carried out in order to cause the electric pump to rotate. The method comprises the stage of regulating the supply voltage as a function of actual operating conditions monitored in the vehicle using the automatic transmission.

[0001] The present invention relates to a control method for an electricpump adapted to provide pressurised operating fluid for an automatictransmission.

BACKGROUND OF THE INVENTION

[0002] Automatic transmissions for vehicles are known in which anelectronic control unit generates signals for the control of a pluralityof actuators of hydraulic type coupled to a clutch and to a gear changeand used to bring about the selection and engagement/disengagement ofthe gears and the opening/closing of the clutch.

[0003] Known automatic transmissions are provided with an electric pumpwhich is adapted to pressurise, in a hydraulic circuit, an operatingfluid (oil) which is then supplied to the actuators in order to providethe power needed to open/close the clutch and select and engage thegears.

[0004] It is also known that in automatic transmissions of known typethere is no control of the speed of rotation of the electric pump; forthis reason, in some operating conditions, the noise generated by theelectric pump during its operation may be particularly intense andperceptible to the driver and/or the other vehicle passengers. Forinstance, in all the situations in which the noise generated by othermembers of the vehicle is low, the noise of the electric pump may beparticularly unpleasant for the driver.

[0005] A number of solutions have been proposed to resolve theabove-mentioned drawback, including:

[0006] using a pump characterised by internal members with very precisegeometries;

[0007] using special materials for the connection joint between theelectric motor and the pump;

[0008] installing housings of sound-absorbing material in the vehicle tocover the pump;

[0009] using supports of the “silent-block” type to secure the pump bodyto the vehicle frame.

[0010] The proposed solutions, although not completely resolving thenoise problem, introduce further component members and entail anincrease in costs.

SUMMARY OF THE INVENTION

[0011] The object of the present invention is to provide a controlmethod for the electric pump which resolves, in a simple manner and at alimited cost, the drawbacks of automatic transmissions of known type.

[0012] This object is achieved by the present invention which relates toa control method for an electric pump adapted to supply pressurisedoperating fluid to at least one actuator of an automatic transmission inorder to cause the opening/closing of the clutch and/or the selectionand engagement of the gears, in which the stage of supply of a voltageto the motor of the electric pump is carried out in order to cause theelectric pump to rotate, characterised in that it comprises the stage ofregulating this voltage as a function of actual operating conditionsmonitored in the vehicle using the automatic transmission.

[0013] In this way, the speed of rotation of the electric pump isregulated as a function of the operating condition detected at thatmoment in the vehicle. It is therefore possible to carry out a speedcontrol and reduce this speed and therefore the noise of the electricpump when it may be perceptible to the driver.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The invention will be described below with particular referenceto the accompanying drawings, which show a preferred embodiment thereof,and in which:

[0015]FIG. 1 is a diagrammatic view of an automatic transmission of amotor vehicle operating according to the method of the presentinvention;

[0016]FIG. 2 shows, in a block diagram, the operations of the method ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0017] In FIG. 1, an automatic transmission (also known as a “robot”transmission) of a motor vehicle (which may be of any type and is notshown for ease of description) is shown overall by 1.

[0018] The engine 2, in particular an internal combustion engine, has anoutput shaft 4 connected, by means of the interposition of a clutch 5,to the input shaft 6 of a gear change 7 having an output shaft 8communicating, via a transmission (not shown), with the wheels of thevehicle (not shown).

[0019] The clutch 5 is coupled to a first actuator unit 10 (of knowntype), in particular an actuator unit actuated hydraulically by means ofpressurised oil, in order to cause the opening and closing of the clutch5. The first actuator unit 10 comprises a power unit 10 a which receivesdrive signals OPEN/CLOSE for the opening and closing of the clutch 5.

[0020] The gear change 7 is coupled to a second actuator unit 12 (ofknown type), in particular an actuator unit actuated hydraulically bymeans of pressurised oil, in order to carry out the operations of gearselection and engagement/disengagement of the gears selected.

[0021] The second actuator unit 12 comprises a power unit 12 a whichreceives drive signals SEL for the selection of the rank of gears andcontrol signals ENG/DIS for the engagement/disengagement of the gearselected.

[0022] The automatic transmission 1 comprises an electronic control unit(ECU) 15 which receives a plurality of information signals In andgenerates as output the above-mentioned drive signals OPEN/CLOSE for theopening or closing of the clutch 5 and SEL, ENG/DIS for the selectionand engagement/disengagement of the gears in the gear change 7.

[0023] In particular, the electronic control unit receives as input aplurality of information signals In measured by sensors 16 and connectedwith the operation of the engine 2 (speed of rotation of the engine,quantity of fuel injected into the engine, torque supplied, etc.), theoperation of the gear change 7 and the course of the vehicle (vehiclespeed, accelerator position, etc.).

[0024] The electronic unit 15 also receives control signals generated bya device 17 that can be manually actuated by an operator (not shown) tocontrol the selection of the different gears. For instance, the device17 may be of a sequential type and used to control a unit increase(UP-SHIFT) of the gear engaged and a unit decrease (DOWN-SHIFT) of thegear engaged. The electronic control unit 15 also receives controlsignals generated by an ignition device 40 (ignition key) that can bemanually actuated by an operator (not shown) for the ignition/cut-off ofthe electronic control unit 15.

[0025] The automatic transmission 1 comprises a device for thegeneration of pressurised operating fluid (oil) 20 which comprises anelectric pump 22 which receives as input operating fluid (oil) from atank 24 (shown diagrammatically) and supplies as output pressurisedoperating fluid to a supply line 25. The supply line 25 communicateswith the first and the second actuator unit 10 and 12, supplying themwith the pressurised oil in order to open/close the clutch and/or selectand engage the gears. The pressurised fluid supply line 25 communicateswith an operating fluid tank 26 (of known type); moreover, a non-returnvalve 30 is disposed between the outlet of the electric pump 22 and theinlet of the tank 26.

[0026] A pressure sensor 33 detects the pressure Pline in the supplyline 25 and supplies the information associated with this pressure Plineto the electronic control unit 15. The information on the line pressurePline is used to control the starting/stopping of the electric pump 22;in particular, the electric pump 22 is actuated when the pressure Plinedetected drops below a lower threshold and is stopped when the pressurePline detected exceeds an upper threshold.

[0027] According to the present invention, the electric pump 22 iscontrolled by a smart drive circuit 35 which communicates with theelectronic control unit 15 and is adapted to control the speed ofrotation of the electric pump 22 as a function of the actual operatingconditions monitored in the vehicle using the automatic transmission 1.

[0028] In particular, the speed control of the electric pump 22 isobtained by varying the actual value Veff of the supply voltage suppliedto the motor (not shown) of the electric pump 22 between a minimum valueVmin (conveniently Vmin is slightly above 0) and a maximum value Vmax(conveniently Vmax=Vbatt, where Vbatt is the voltage supplied by thevehicle battery).

[0029]FIG. 2 shows the operations performed by the electronic controlunit 15 together with the smart drive circuit 35 for the regulation ofthe speed of rotation of the electric pump 22.

[0030] In the first block 100, it is checked whether the engine 2 isoff; if so (engine 2 off), the block 100 is followed by a block 110 andif not (engine 2 on) the block 100 is followed by a block 120.

[0031] The block 110 checks the position of the vehicle ignition key 40;in particular, if the ignition key 40 is disposed in a first position(OFF) in which the engine and the electronic unit 15 are not beingsupplied as normal, the block 110 is followed by a block 130 whichcontrols the supply of the motor of the electric pump 22 with a firstvoltage V₁ which achieves a speed of rotation n₁ of the electric pump22.

[0032] If, however, the ignition key 40 is disposed in a second position(ON) in which the engine 2 and the electronic unit 15 are beingsupplied, the block 110 is followed by a block 140 which checks whethera gear change operation is under way.

[0033] When the block 140 does not detect that a gear change operationis under way, the block 140 is followed by a block 150 which controlsthe supply of the motor of the electric pump 22 with a second voltage V₂which achieves a second speed of rotation n₂ of the electric pump 22.When, however, the block 140 detects that a gear change is under way,the block 140 is followed by a block 160 which controls the supply ofthe motor of the electric pump 22 with a third voltage V₃ which achievesa third speed of rotation n₃ of the electric pump 22.

[0034] The block 120 detects whether the engine 2 is in the ignitionstage; if so (engine 2 in the ignition stage), the block 120 is followedby a block 170 which controls the supply of the motor of the electricpump 22 with a fourth voltage V₄ which achieves a fourth speed ofrotation n₄ of the electric pump 22.

[0035] When the engine 2 is not in the ignition stage (and is thereforealready in motion), the block 120 is followed by a block 180 whichchecks whether the vehicle is quasi-stationary, i.e. if the speed of thevehicle is below a threshold; if so (vehicle stationary or travelling atlow speed), the block 180 is followed by a block 190 and if not (vehicletravelling at a speed above the threshold), the block 180 is followed bya block 200.

[0036] The block 190 checks whether a gear change operation is underway.

[0037] When a gear change operation has not been detected, the block 190is followed by a block 210 which controls the supply of the motor of theelectric pump 22 with a fifth voltage V₅ which achieves a fifth speed ofrotation n₅ of the electric pump 22. When, however, the block 190detects that a gear change is under way, the block 190 is followed by ablock 220 which controls the supply of the motor of the electric pump 22with a sixth voltage V₆ which achieves a sixth speed of rotation n₆ ofthe electric pump 22.

[0038] The block 200 controls the supply of the motor of the electricpump 22 with a seventh voltage V₇ which achieves a seventh speed ofrotation n₇ of the electric pump 22.

[0039] There is a return to the block 100 after the blocks 130, 150,160, 170, 210, 220 and 200.

[0040] It will be appreciated that the supply voltages provided arerelated to one another with the ratio:

[0041] V₇>V₆>V₅>V₄>V₃>V₂>V₁.

[0042] Preferably, but not exclusively, V₇=V_(batt) and V₁=V_(min) ofslightly above zero such that the speeds achieved are of the type:

[0043] n₇>n₆>n₅>n₄>n₃>n₂>n₁.

[0044] In this way, the electric pump is supplied with a low voltage(and rotates at a low speed) when the engine is off and therefore thenoise generated by the electric pump is more perceptible, while theelectric pump is supplied with a voltage close to the maximum voltage(and rotates at high speed) when the engine is on and therefore thenoise generated by the electric pump is less perceptible.

[0045] Moreover, when a gear change is under way (blocks 140 and 190),the speed of rotation of the electric pump is increased in order tosupply greater hydraulic power.

[0046] In this way, the electric pump 22 is supplied by a voltageregulator which provides different voltages (V₁, V_(2,) V_(3,) V_(4,)V₅, V₆ and V₇) so as to obtain respective different speeds of rotation(n₁, n₂, n₃, n₄, n₅, n₆ and n₇), each of which is associated with aparticular operating situation detected in the vehicle.

[0047] The operating situations detected and the respective speedsimplemented are as follows:

[0048] engine 2 off (block 100—YES) and vehicle key in OFF position(block 110—OFF): the speed of rotation of the electric pump 22 iscontrolled to the predetermined value n₁ (block 130);

[0049] engine 2 off (block 100—YES), vehicle key in ON position (block110—ON) and no gear change operation taking place (block 140—NO): thespeed of rotation of the electric pump is controlled to thepredetermined value n₂ (block 150);

[0050] engine 2 off (block 100—YES), vehicle key in ON position (block110—ON) and gear change under way (block 140—YES): the speed of rotationof the electric pump is controlled to the predetermined value n₃ (block160);

[0051] engine 2 at ignition stage (block 120—YES): the speed of rotationof the electric pump is controlled to the predetermined value n₄ (block170);

[0052] engine 2 in rotation at a speed close to idling, vehiclequasi-stationary (block 180—YES) and no gear change operation under way(block 190—NO): the speed of rotation of the electric pump is controlledto the predetermined value n₅;

[0053] engine 2 in rotation at a speed close to idling, vehiclequasi-stationary and gear change under way (block 190—YES): the speed ofrotation of the electric pump is controlled to the predetermined valuen₆ (block 220).

[0054] The speed of rotation implemented by means of the operations ofFIG. 2 may be subject to correction operations; in particular, when theengine 2 is in rotation at a speed close to idling and the vehiclewindows are open, the speed of rotation calculated may be reduced by apercentage value (for instance 20%) with respect to the value set by theblocks 130, 150, 160, 170, 210, 220 or 200.

[0055] When, however, the temperature of the electric pump (measured orestimated) is greater than a predetermined threshold, the speed ofrotation of the electric pump may be increased (for example by 20%) withrespect to the value provided and set by the blocks 130, 150, 160, 170,210, 220 or 200.

[0056] Lastly, during the initial stage of actuation of the electricpump, the speed to which it is set may be increased gradually, in apredetermined time interval, from a zero value to the speed valueprovided for the specific operating situation and calculated by theblocks 130, 150, 160, 170, 210, 220 or 200. This provides a furtheradvantage since the gradual increase of the voltage applied to theelectric pump prevents the formation of the current peak that may begenerated in automatic transmissions of known type in the initialinstants of actuation of the electric pump.

[0057] This prevents any disturbance of other electrical systemsinstalled on board the vehicle (it is known, for instance, that thecurrent peak may cause the phenomenon of flickering of the vehiclelights). In this way it is possible to eliminate the initial currentpeak without substantially delaying the supply of a flow of hydraulicoil.

[0058] It will be appreciated from the above that the present inventionhelps to reduce the electric pump noise to a level appropriate to theoperating situation (engine off, engine idling, vehiclequasi-stationary, windows open, etc.) of the system.

[0059] This noise reduction is obtained without acoustically insulatingthe electric pump, i.e. with an evident saving of costs arising fromacoustic insulation. It is therefore possible to use less costlyelectric pumps that do not have to guarantee very restrictive maximumnoise levels.

[0060] The present invention also makes it possible to limitdisturbances of the electrical plant of the vehicle caused by the pumpactuation stages.

[0061] It will lastly be appreciated that modifications and variationsmay be made to the above description without thereby departing from thescope of protection of the present invention.

1. A control method for an electric pump (22) adapted to supplypressurised operating fluid to at least one actuator (10, 12) of anautomatic transmission (1) in order to cause the opening/closing of theclutch and/or the selection and engagement of the gears, in which thestage of supply (35) of a voltage to the motor of the electric pump iscarried out in order to cause the electric pump to rotate, characterisedin that it comprises the stage of regulating (130, 150, 160, 170, 210,220, 200) this voltage as a function of actual operating conditionsmonitored in the vehicle using the automatic transmission (2).
 2. Amethod as claimed in claim 1, in which different voltages are generated(V₁, V₂, V₃, V₄, V₅, V₆ and V₇) for the supply of the electric pump soas to obtain respective different speeds of rotation (n₁, n₂, n₃, n₄,n₅, n₆ and n₇) , each voltage being selected in conjunction with arespective operating situation detected in the vehicle.
 3. A method asclaimed in claim 2, in which a first operating situation is detected inwhich the engine (2) of the vehicle is off (100) and there is no enginesupply signal (110), the speed of rotation of the electric pump (22)being set to a first predetermined value (n₁) in the presence of thisfirst operating situation.
 4. A method as claimed in claim 2, in which asecond operating situation is detected in which the engine (2) of thevehicle is off (100), there is an engine supply signal (110) and no gearchange operation is under way, the speed of rotation of the electricpump (22) being set to a second predetermined value (n₂) in the presenceof this second operating situation.
 5. A method as claimed in claim 2,in which a third operating situation is detected in which the engine (2)of the vehicle is off (100), there is an engine supply signal (110) anda gear change operation is under way, the speed of rotation of theelectric pump (22) being set to a third predetermined value (n₃) in thepresence of this third operating situation.
 6. A method as claimed inclaim 2, in which a fourth operating situation is detected in which theengine (2) of the vehicle is at the ignition stage (120), the speed ofrotation of the electric pump (22) being set to a fourth predeterminedvalue (n₄) in the presence of this fourth operating situation.
 7. Amethod as claimed in claim 2, in which a fifth operating situation isdetected in which the engine (2) of the vehicle is in motion (120), thevehicle is travelling at a speed lower than a threshold and no gearchange operation is under way, the speed of rotation of the electricpump (22) being set to a fifth predetermined value (n₅) in the presenceof this fifth operating situation.
 8. A method as claimed in claim 2, inwhich a sixth operating situation is detected in which the engine (2) ofthe vehicle is in motion (120), the vehicle is travelling at a speedlower than a threshold and a gear change operation is under way, thespeed of rotation of the electric pump (22) being set to a sixthpredetermined value (n₆) in the presence of this sixth operatingsituation.
 9. A method as claimed in claim 2, in which a correctionstage is carried out in which the speed of rotation set is modified as afunction of further operating parameters that are detected.
 10. A methodas claimed in claim 9, in which the correction stage comprises the stageof reducing the speed of rotation with respect to the set value (130,150, 170, 170, 210, 220, 200) when the engine (2) is in rotation at aspeed lower than a threshold and the vehicle windows are open.
 11. Amethod as claimed in claim 9, in which the correction stage comprisesthe stage of increasing the speed of rotation with respect to the setvalue (130, 150, 170, 170, 210, 220, 200) when the temperature of theelectric pump is greater than a predetermined threshold.
 12. A method asclaimed in claim 9, in which the correction stage comprises the stage ofgradually increasing, over a predetermined time interval, the speed ofrotation from an initial value, in particular a zero value, to the speedvalue provided for the particular operating situation.